Multilayer interconnect structures have been developed for dense electronic packaging assemblies. A multilayer interconnect structure generally includes a plurality of metal layers that define the interconnects including, for example, both vertical and horizontal interconnects, and a plurality of dielectric layers that separate the metal layers. For high frequency applications, such as for monolithic microwave integrated circuit (MMIC) devices, the dielectric layers may be formed of an organic polymer, as opposed to an inorganic polymer, since a dielectric layer formed of an organic polymer creates less loss at the higher frequencies.
One organic polymer that may be utilized as a dielectric layer between the metal layers of a multilayer interconnect structure is benzocyclobutene (BCB). In this regard, BCB has a relatively low dielectric constant of 2.65 and a relatively low loss tangent of 0.0001 for signals in the microwave region. As such, a multilayer interconnect structure having BCB dielectric layers may have less parasitic capacitance between both the horizontal and vertical interconnects a high frequencies, such as frequencies in the microwave and millimeter wave ranges than multilayer interconnect structures utilizing other types of dielectric layers.
At least some electronic devices that are configured for operation at relatively high frequencies may include a semiconductor layer comprised, for example, of a III-V material, such as gallium nitride (GaN), formed on an underlying substrate, such as a silicon carbide (SiC) substrate. The semiconductor layer may define a plurality of transistors that define the functionality of the electronic device. The multilayer interconnect structure may then be formed on the semiconductor layer. However, BCB has relatively poor adhesion with III-V materials, such as GaN. In this regard, BCB has a relatively large mismatch in the coefficient of thermal expansion with respect to GaN and other III-IV materials.
BCB may also have poor adhesion to the metal interconnects of a multilayer interconnect structure. In this regard, for devices configured to operate at high frequencies, the metal interconnects may be formed of gold since gold has a relatively low resistive loss at high frequencies. However, BCB also has a relatively poor adhesion with respect to gold interconnects.
Adhesion promoters, such as AP3000 developed by The Dow Chemical Company, may be utilized to facilitate adhesion between BCB and a GaN layer. However, adhesion promoters do not increase the adhesion between BCB and the gold interconnects and, as a result, multilayer interconnect structures utilizing BCB to form the dielectric layers may still suffer from poor adhesion.
Poor adhesion of the BCB dielectric layers may manifest itself in delamination of the BCB dielectric layers. In this regard, the manufacturing process of an electronic device having a multilayer interconnect structure that includes BCB dielectric layers may include the exposure of the electronic device to various solvents, such as during an acid wash. As a result of the poor adhesion between the BCB layers and the gold interconnects and solvent may migrate, as a result of capillary action, between the BCB layers and the gold interconnects and, in some instances, between the BCB layer and the GaN layer, thereby creating delamination of the BCB layers. Such delamination may cause the electronic device to be unacceptable such that the electronic device must be scrapped. As the delamination may not occur until toward the end of the manufacturing process during the exposure of the electronic device to various solvents, delaminations may be particularly costly, as the electronic device has already been subjected to the majority, if not all, of the manufacturing processes prior to the occurrence of the delaminations.